In such a turbojet, mechanical drive to at least one of the compressor wheels must be transmitted inwardly from the periphery of the turbojet rather than outwardly from a central shaft. In other words there must be an outer rotor assembly as well as an inner rotor assembly. Driving the wheels that depend from the outer rotor presents a problem which up to the present has not been solved adequately for contrarotating turbojets to enable them to be implemented on an industrial scale.
Driving these wheels from their periphery leads to the blades transmitting mechanical forces. However, the blades are shaped mainly as a function of aerodynamic considerations: in particular these require the blades to be extremely thin to satisfy aerodynamic conditions, especially when the air flow is supersonic, and such blades are generally unsuitable for transmitting mechanical drive forces.
Further, while the ends of the blades in turbojets that do not use contrarotation are free, proposed embodiments of contrarotating wheels call for the blades to be fixed not only at their inner ends, ie. where closest to the axis, but also at their outer ends. When the turbojet is in operation, the inner and outer fixed ends are at different temperatures, thus introducing stress factors of thermal origin and an additional source of deformation.
Preferred embodiments of the present invention eliminate the above-mentioned drawbacks.